compact carrier for Kossel Deltas

Based on Miltons Delrin sliding carrier, I thought of a smaller more compact version.
It is based on two angled profiles with a shoulderlength of 15x15mm. They are superglued together to build one T-profile tower.
Two pieces of cylindric Delrin are slotted vertically to fit onto the tower profile.
The carrier has snap in cavities for the delrin pieces and the corners are thinned out to allow some tension.
The trapeziodal shape of the carrier helps to keep the carrier centered



The stepper will be mounted below the tower in such way, that the belt ( not shown yet ) runs through the carrier.
The mounting hole on the side is for Traxxas rod ends ( 40mm rod distance )

Any opinions or suggestions?

edit1: I changed the title, because the compact_carrier would also work with 2020 extrusion on bigger Deltas

Edited 4 time(s). Last edit at 11/02/2017 05:06AM by o_lampe.

My suggestions:

- Make the sliding carrier taller. Any horizontal tilt of the carriage will cause calibration issues. A taller carriage will reduce the risk or amount of tilt.

- Why not PTFE instead of Delrin?

- Why not use T-profile aluminium instead of gluing two L-profile pieces together?

- 40mm spacing is very low. Even the original Mini Kossel uses more than 40mm AFAIR (but I could be wrong, it's a while since I had one). Larger spacing gives more stability, and there is no point in going so small that the cooling fans etc. on the effector collide with the belts before the effector does.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

T-profile would be nicer, but I haven't found it yet in the right size.
Same to PTFE, I found POM ( Delrin ) or Polyamid rods. ( I admit, I haven't been searching hard)
Increasing carrier height is easy, maybe use 4 sliders per tower in total ( like Miltons carriers )
40mm is the width of the carrier, the rods will have 47mm distance. It'd fit my standard sized effectors.

Edited 2 time(s). Last edit at 10/31/2017 02:09PM by o_lampe.

Love it! great idea to try something other than aluminum extrusion!

Delrin is denser than PTFE, which is a bit spongy and will create more contact area for more friction with less accuracy. Delrin specifically over knock off brand Acetel from my research was higher durometer and therefore more appropriate. I just recently got some of the PTFE infused version of Delrin Acetel, it has PTFE in if for low friction specificly for use as a bushing, I found it was not noticeably better than the normal Delrin though, and it's brown which does not look nearly as nice as the white standard Delrin rod.

dc42 is so right on the effector size, 40mm is as tight as you can go without huge issues with fans under the effector.

I think slotting round objects precisely is hard, even in a mill with V blocks. That design would slide nicely but it needs to be able to settle into position without losing accuracy. round object sliding on rails with slight compression will do that but an internal rail will make space that cannot be filled. Between adding processing time of the material and making alignment part of that process, I would stick with the fairly accurate round surface of the Delrin rod as a base to build accuracy from.

One thing I am not so happy about with my original design is the absolute parallel between the extrusion inward face and the carriage. I used compression on the bushing and accurate CAD with many revisions to get something that stays fairly parallel within the range of flex applied to the printed parts holding the bushings as a screw compresses the bushing into the extrusion channel. this could be improved with the bushing in a slot in the carriage bracket arms around the extrusion and compression being applied by a separate part. this to allow the bushing to move in towards the extrusion without flexing the part guiding it, only the part pushing it. Working on that design and will share when I have something functional.

Edited 2 time(s). Last edit at 10/31/2017 02:39PM by Milton.

Thanks for sharing your experience with PTFE/Delrin mix. I stick with Delrin.
Slotting the sliders is also not in my comfort zone, but the only other extrusion profile, I can think off is a double-T or H-profile. But I'm not sure, if that would be stable enough? It is 8x20, which would make the trapez-shape even more stable.

The effector can be huge even when rod distance is small. But in such a small printer I wouldn't install part fans below the effector. Why not place them around the bed in a campfire tornado pattern?



This pic is just a vague draft version off how a H-profile could be used. The rod ends will probably bind (maybe Magballs are better suited?) and the belt running through the profile needs a clever idea to connect it with the carrier.

Edited 2 time(s). Last edit at 11/01/2017 04:52AM by o_lampe.

I think you're onto something. It took me a lot of revisions to get my design, went from flat sections of UHMD cutting board material as runners (not great but has potential, may revisit for cement laying house building delta) then moved on to delrin rod. The round shape works with an aluminum extrusion T slot to create the same angles of resistance to twisting that are seen in diagrams of good 4 channel rails. I think it was around 2-3 weeks before I had something I really felt was going to actually work like a sliding carriage on wheels bearings. For this H or L framing material maybe use several section of the delrin rod around it, on different planes. Or even maybe flat delrin, if it available, or PTFE but flat sections might also work. maybe remember the stuff is like a few cents for a 1 inch section, so you can use more than 2 at the top and bottom of the carriage. PTFE is nice and very low friction, I specificly needed the highest durometer due to the geometry of the forces with twisting off axis torque and the T slot edges, if it spread out and gripped more as it was compressed and twisted it would have increasing friction and twist more. If it is running on a flat plane and resisting that plane only, it could be different material with different properties. flat thin PTFE might be better, if there is such a thing as PTFE sheet, the less dense material would not matter as much as it would not be riding on a rounded edge but resisting a flat plane.

You are probably right about using flat Delrin. The cylinder just runs on the edge of the H-profile, wearing out pretty fast.
A well milled piece of Delrin could act as belt clamp and run on the face of the profile... I see a mushroom shaped slider, the rear part still able to align itself in the carrier.

Back to the drawing board

make 3d printed prototype, get samples of material for towers, try things as you think of them before you get to caught up in trying to pick them apart. Then be rational and honest about what you have done right and wrong. Its sort of defined for this project as we have examples of a standard of performance from cheaper rails and V-wheels that is not really hard to surpass just by having no moving parts between the carriage and the rail. If it slides smoothly and stiction is accounted for and overcome, there is nothing else to trouble shoot IGUS website has a nice engineering guide for polymer bushings and distances to sliding points and pulling points to eliminate stiction, I think this is not the link I used the graphic is different but the information is the same and there is other information as well.

IGUS bushing common mistakes in design page

My design all started with actually getting the 1515 extrusions for making a Delta after loving my i3 clone for a few months. I went to industrial design university and figured 'I should be able to build a 3d printer, and Delta seems great as its print doesn't move'. I bought the extrusions planning on getting rails and was shopping 2 and 4 channel rails. I realized for the investment for actual high quality rails I would want a bigger build area than a mini kossel so I started designing my own linear motion as a design process exercise. I honestly planned on buying rails soon after but needed the practice as I am out of school now.

The ability to print prototypes made it all possible. Truly a RepRap printer it came from an i3 clone and prints almost all its own parts. I can't wait to see wait kind of 'RepMotion' parts you come up with for your printer design. Maybe think about what kind of material can ba had in 2-3 foot lengths that is very straight and has a surface quality that allows it to be a rail, that is a fundamental aspect of this, smooth surface for the bushing to glide on.

The biggest key is make lots of prototypes, which I bet you're good at since you 3d print LOL. Don't discount an idea that had some aspect you liked, try it out. Even if you already know it's not a final design seeing it in action will feed your creativity and help understand how the positive aspects of the design can be carried forward will the negative ones left behind.

I have Delrin and PTFE in round bar, flat and sheet. It is why I prefer Igus .
Igus filament is not cheap but you can make a lot of various bearings and lead screw nuts that fits perfectly !
Igus can run on anodized Al and some carbon fiber profile. A definite plus.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

I've made printed sliders from PETG, the rougher surface can be a plus because it reduces contact area and thereby friction. For sure an option, when no CNC mill is at hand. The small size of the slider would be a challenge, tho...


Here's another teaser: I tested the possibility to run a 6mm GT2 belt through a 2020 extrusion with a 10mm idler. There is plenty of room for the belt, so chances are good the compact_carrier (TM) would work for bigger Kossel Deltas as well. The gain of a few extra mm in workspace/printersize is neglectible, but placing rod ends, belts and sliders closer together sure is an advantage to consider. ( and it looks cleaner with invisible belts, too )



Edited 1 time(s). Last edit at 11/02/2017 05:00AM by o_lampe.

nice idler setup. yes with bushings or anything sliding the ratio of offset from the drive to the points of contact is a huge issue and the closer the better.

I was curious if there'd be any problems mounting the stepper below the extrusion, but a standard NEMA17 fits nicely between the legs of a Delta triangle.
I'll print the corners and a makeshift belt clamp tomorrow.

@Milton, do you see a chance to route a 6mm belt through openbuild 15x15 extrusions?
Alternatively I've seen 3mm wide GT2 belt and pulleys. Maybe they will not stretch too much in a small Delta?

The compact_corner is a mess to assemble! Like a japanese puzzle box...
Version 5 is finally manageable, but I still have to use certain screws without alternative. Not very user friendly...but so much smaller!



Haven't had time to think about a useful belt clamp.

I made a first version of the belt clamp. It requires a closed loop belt. Five teeth have to be removed before it fits in the gap. Then the belt keeps itself from slipping.
It is printed in PETG with a 0.8mm nozzle and even with such a coarse setup, it fits perfect in a Item slot 5 compatible 2020 extrusion.

Next I have to add some Delrin slider brackets, without limiting the rods area.

I've made a version of the belt clamp with mushroom shaped Delrin sliders. I printed a dummy version of it in PETG and after removing the "elefant feet" and treating the extrusion with a heatgun, the dummy runs surprisingly smooth. I slid it a few times across the hot extrusion until excessive tension was literally ironed out.

I have ordered Delrin and also PTFE rods, but it feels like it could be printed as well. ( Even more so, if I'd print it with a 0.4 nozzle )

Just noticed that the part in the picture is upside down. The way you'd print it.

Edited 3 time(s). Last edit at 11/05/2017 12:04PM by o_lampe.

wow nice work. You could buy some iglide filament from IGUS if you're going to print bushings. I haven't seen anyone do that yet so it would be really cool and helpful to get some community feedback on I glide for delta bushings. Just checked the IGUS webpage, but hard to navigate but if I understand correctly some of their filament is around $60 for 250grams, which seems ridiculously expensive... but then again, bushings are small 250gm could go a long way.

A little update:
After trying to print some decent sliders, I bit the bullet and milled a rig for the delrin and PTFE rods. ( My mill is still a work in progress, so I expected the worst )
The ptfe rod was a hit right away. It slides easily and has no play.
Later I milled the delrin rod in two passes, but made a calculation mistake. It fits nicely too, but is off center. Luckily I have another piece of Delrin to try again.
I noticed, the rod curved after I removed it from the rig. Maybe it got overheated?

I changed the design of the slider again to make it easier to hit the sweet spot. I call it slotted mushroom.
Again, I tried to print the new design but wasn't successful ( 0.6 nozzle, PETG, 1st. layer issues with Lokbuild )
Anyway, if someone is interested to print a slider to get a feel of the pros/cons compared to v-wheel or linear rails, I attached the .stl
It's made for 5mm slot, but you can easily scale it to match your extrusion.
I'd really like to get some feedback.

There's also a 2020-frame waiting for the closed loop belts and some working compact-carriers. The stepper is removable after the frame is assembled. It's screws are accessible from the front. A big plus compared to robotdigg corners



The opening in the bottom corner looks like a doghouse. I'm searching for a matching name for this type of Delta, since it isn't a Rostock or Kossel.

Doghouse Delta
Mushroom Delta
Compact carrier Delta

What do you think?

How is the belt tension maintained?

Doghouse Delta!

Edited 1 time(s). Last edit at 11/20/2017 12:08AM by firefly555.

Thanks for voting firefly555!
I can adjust the belts with the t-nuts in the corners. Just have to make sure the endstops are all at the same height.

I made some progress with printed mushroom parts. I placed them like that:


After deburring, I treated them with the heatgun ( as described above ). Now they slide very easy with no play.
I also decided to split belt clamp and slider. Just to keep the rod to rod distance constant, no matter how much the slider is stretched.

Another problem solved: I can now use open belts, so tower height is no longer restricted.
I simply added a second belt clip below the slider clamp. The cutoffs for the belt teeth came out pretty good, even with 0.6 nozzle and PETG.



The pic doesn't show the slicing position, it's just to show the two piece compact carrier in the right mounting position.

Edited 1 time(s). Last edit at 11/21/2017 03:06AM by o_lampe.

Not meaning to be a naysayer since I do generally like this idea, but that lower belt clip is going to snap off in no time at all, unless you intend to have almost no belt tension.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

You are right, it already snapped.
I thought, I could save some length, but in PETG it has to be thicker. The final goal is to mill the belt clamp parts from aluminum and put the slider clamp in a sandwich between.
The good news is, there is plenty of room below the rods, since the carriers will never move down to the bottom corner.

Yeah I find in ABS those type of belt clamps need to be at least 7 teeth and quite heavily reinforced both sides, but then as a prototype for a metal carriage, it'll do the job.

Edited 2 time(s). Last edit at 11/21/2017 06:25AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

If I were designing my own carriages, I think I would design it to have a twist in the belt on the return side. That avoids the need for toothed idlers, and also means that the teeth on the two ends of the belt can lock into each other so that the carriage doesn't carry the belt tension. The Ormerod uses this design on its X carriage, and it works very well. Here [www.thingiverse.com] is an OpenScad model of the carriage.

Edited 1 time(s). Last edit at 11/21/2017 06:34AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I will probably get critiqued for this, but with my PCB carriages on my kossel XL, I do not have robotdigg carriages or anything like that on top of them, that's unnecessary complexity and mass. One of the 4 screw holes in the linear rail carriage now sports a 25mm M3 screw, which both sides of my belt are fixed to, with a twist for the top pulleys, so that as DC said the tension is carried by the belt. Ill append an image later.

As for tensioning, I have printed inline tensioners, which work great on deltas as there is so much "spare" belt below the carriages which does not interfere with anything in use that you don't get on corexy's/cartesians, although I'd like to use them there also, as its just one twist of a screw to tension.



Edited 2 time(s). Last edit at 11/22/2017 03:41AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Thanks for your comments.
Twisting the belt is no option in the 2020 extrusion. There's more room in the H-profile, but I want to keep the design the same for both protos.

I thought of glueing a short piece of belt as a connector between the open ends, but even that isn't possible in 2020.

While we are talking about the belt routing: Is it neccessary that the upper idler has the same diameter than the drive pulley? In other words: does the belt have to run parallel up and down? Or is it similar to CoreXY belt routing, where only the belt parts that change their length, have to be parallel to the carrier? (none in a Delta )

The belt should be straight between the drive pulley, carriage and idler on the working side, it doesn't matter about the return side.

If it was not (and mine in the image above is slightly not straight) then you will get a different amount of carriage travel per step depending on the carriage position. Having my belt fixed maybe 2mm off centre over a 1000mm travel is probably not going to show up in my prints.

I should use better belt clamps than cable ties but to be fair they do work.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
I will probably get critiqued for this, but with my PCB carriages on my kossel XL, I do not have robotdigg carriages or anything like that on top of them, that's unnecessary complexity and mass. One of the 4 screw holes in the linear rail carriage now sports a 25mm M3 screw, which both sides of my belt are fixed to, with a twist for the top pulleys, so that as DC said the tension is carried by the belt. Ill append an image later.

As for tensioning, I have printed inline tensioners, which work great on deltas as there is so much "spare" belt below the carriages which does not interfere with anything in use that you don't get on corexy's/cartesians, although I'd like to use them there also, as its just one twist of a screw to tension.

[attachment 99816 20171121_22265601.jpg]

What an elegantly simple solution! It could be tidied up by attaching a printed block using the 2 screws on the right of the carriage, and locking the belts into a slot in that block as on the Ormerod carriage.. That would also move the belt left a little, to keep the belt straight.

Edited 2 time(s). Last edit at 11/22/2017 04:35AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].